It is known that penicillin antibiotics inhibit the growth of various grampositive and gramnegative bacteria. It is further known that only few penicillins have a good activity against important gramnegative problematic germs, such as Pseudomonas and Klebsiella, which occur primarily in hospitals. During the last years the frequency of occurrence of infections which are caused by these germs, particularly by Pseudomonas, has increased steadily. While penicillin derivatives such as Carbenicillin (U.S. Pat. No. 3,142,673), Sulbenicillin (U.S. Pat. No. 3,660,379) as well as Ticarcillin (U.S. Pat. No. 3,282,926) are described as antipseudomonal antibiotics, they show in vivo as well as in vitro only a poor activity. An important further development are acylated derivatives of .alpha.-aminobenzylpenicillins, e.g. Ampicillin and Amoxycillin. These kinds of compounds have been intensively studied during the last years, and as a result Azlocillin, i.e. 6-{D-.alpha.-[(2-oxoimidazolidine-1-yl)carbonylamino]-4-phenylacetamino}-p encillanic acid sodium salt (e.g. Belgian Pat. No. 767,647), has recently been introduced on the market as a further antipseudomonas penicillin. For a successful treatment, however, this penicillin must be administered at high dosages. Moreover, it has only a moderate activity against Klebsiella and various kinds of E. coli. Therefore, it is still a need to search for new penicillins having an increased effectiveness against bacteria such as Pseudomonas resp. Klebsiella and E. coli.
While, as mentioned above, much research work has been and is still being done concerning acyl derivatives of .alpha.-aminobenzylpenicillins, there is little knowledge about derivatives in which a heterocycle is attached over a ureido bridge. ##STR2## to the .alpha.-benzyl carbon atoms of .alpha.-amino-benzylpenicillins. Only in German Offenlegungsschriften Nos. 2,450,668 and 25 35 655 and in U.S. Pat. No. 4,031,230 hydroxypyridylureido-benzyl-penicillins of the formula ##STR3## are disclosed. These compounds are nearest in their structure to the novel penicillins of the present invention. As shown in table I below, a number of the novel penicillins according to the present invention distinguish themselves by a significantly stronger antibacterial activity, particularly against bacteria such as E. coli, Pseudomonas and Klebsiella.